How to connect 2 meshes without messing up the textures?
By "old version" I assume you mean 2.79?

What you're looking for is a UV seam. This will prevent the connecting mesh from insisting on bridging between your two original shapes directly, and allow you to position it individually.

For 2.79, select the edge between your connection and your original shape; then hit CTRL+E. You should have the option "Mark Seam" available. This should disconnect the UV map along the corresponding edge, so you can move its vertices independently of the others.

For further details, consider reading the documentation on it for 2.79.